Crystal structure of tert-butyl 3,6-diiodocarbazole-9-carboxylate

The crystal structure of tert-butyl 3,6-diiodocarbazole-9-carboxylate features intermolecular π–π interactions, as well as both type I and type II intermolecular I⋯I interactions.


Chemical context
Derivatives of the carbazole ring system have been used in a wide variety of applications ranging from organic light-emitting diodes (Uoyama et al., 2012) to cell membrane targeting fluorescent probes (Wnag et al., 2023) to compounds that are able to influence the supramolecular structure of G-rich DNA sequences (Debnath et al., 2016). Our group's interest in this molecular entity was inspired by the work of de Bettencourt-Dias and co-workers who have used carbazole derivatives as antennas to sensitize the luminescence of lanthanide metals (Monteiro et al., 2017(Monteiro et al., , 2018(Monteiro et al., , 2020(Monteiro et al., , 2022. Our group was working to derivatize carbazole for use in related lanthanide luminescence applications when compound I, a synthetic intermediate in our work, serendipitously crystallized in an NMR tube.

Database survey
A search of the Cambridge Structure Database (CSD version 5.43 with updates through June 2022; Groom et al., 2016) for structures containing the carbazole ring system substituted with any halogen atom at the C5 and C11 positions (as numbered in Fig. 1) returned 101 hits. The structures CEYXAI (Malecki, 2018) and FUMLIK (Radula-Janik et al., 2015) are closely related to that of compound I with iodine atoms at the C5 and C11 positions, but where the nitrogen atom has been alkylated with either a butyl or benzyl group. A depiction of the supramolecular pillars using a ball-and-stick model with standard CPK colors (I = purple). The left portion of the figure shows the pillars with a view that is aligned with the plane of the aromatic carbazole system, the right portion of the figure shows the same molecules tilted slightly along the b axis. Theinteractions described in the text are depicted with purple dotted lines and the unit cell is drawn with a solid black line.

Figure 1
The molecular structure of compound I, with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level using standard CPK colors (I = purple).
Structure ECUNUM bears bromine atoms at the C5 and C11 positions with a phenylcarbamate group on the nitrogen atom (Duan et al., 2006). A derivative of compound I that bears two iodine atoms in the same positions and a hydrogen atom bonded to the nitrogen atom has been solved as structure YAYDUZ (Xie et al., 2012). Lastly, the di-iodo carbazole has been used as a ligand in a copper(I) complex as demonstrated by Kim and co-workers (ZASYUQ; Kim et al., 2017).

Synthesis and crystallization
The title compound was prepared according to the procedure published by Lee and co-workers (Moon et al., 2007). The compound was dissolved in CDCl 3 and the crystals studied here grew as the solvent slowly evaporated from the NMR tube.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. All hydrogen atoms bonded to carbon atoms were placed in calculated positions and refined as riding: C-H = 0.95-1.00 Å with U iso (H) = 1.2U eq (C) for aromatic hydrogen atoms and U iso (H) = 1.5U eq (C) for the hydrogen atoms of the methyl group.   ; program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: CrystalMaker (Palmer, 2007); software used to prepare material for publication: Olex2 (Dolomanov et al., 2009;Bourhis et al., 2015).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.